In recent years, in an electrophotographic apparatus, such as a copying machine or an optical printer, as a charging method for charging a photoconductor, a dielectric body, or the like, a direct charging method has been employed. The direct charging method is a charging method in which a member (charging member) is placed close to or is brought into contact with a surface of a drum-shaped electrophotographic photoconductor to charge the surface thereof by voltage application. In general, in operation, a rubber roller-type charging member (hereinafter referred to as “charging roller”) formed of a conductive support and a conductive elastic layer provided thereon is pressed against a photoconductor while being rotated.
In such a charging roller, in order to uniformly charge the photoconductor, it is required to ensure a uniform contact of the roller with the photoconductor in a roller axis direction. However, when the charging roller is pressure-pressed against the photoconductor for a long period of time, deformation which is not easily recovered, that is, a compression set (hereinafter also simply referred to as “C set”), is generated at a part of the charging roller in some cases.
When a charging roller on which a C set is generated is used for contact charging, and a part thereof at which the compression set is generated passes a nip portion formed with a photoconductor drum, discharge generated in a space between the surface of the charging roller and the surface of the photoconductor drum is destabilized. As a result, charging irregularities are generated on the photoconductor drum, and defects, such as stripes, are generated in an electrophotographic image in some cases.
PTL 1 has disclosed a method for forming a low friction surface layer having a high hardness on a surface of an elastic layer by adding an additive of a fluorine-based block copolymer or a silicone-based block copolymer to a binder.